The present invention pertains to the manufacture of blanks of corrugated paperboard, solid fiberboard and similar materials and, more particularly, to an apparatus for stripping the scrap portions from die cut blanks used in the manufacture of boxes, cartons and the like.
Blanks of various sizes and shapes, from which boxes, cartons and similar structures are ultimately formed, are die cut from sheets of corrugated paperboard, solid fiberboard or other paper materials. In the die cutting operation, various portions on the interior of the die cut blank may also be cut to different sizes and shapes to provide openings, slots or the like required to enable the blank to be subsequently folded to form a box or similar structure. The die cut interior portions result in scrap which must be removed from the blank in a stripping operation. The manner in which the scrap is stripped from the blank generally depends upon the die cutting method used.
Die cutting may be done by either the flatbed method or the rotary method. A flatbed die cutter utilizes a cutting tool which makes a linear stroke in one position against a flat backing plate or anvil. In a rotary die cutter, the cutting die or dies are mounted to the periphery of a cylindrical roll and the sheet from which the blank is cut is fed between the die roll and a counterrotating backing or anvil roll. In either process, the scrap portions are retained in the blank after cutting and must be mechanically stripped therefrom.
The stripping process in a flatbed die cutting operation usually comprises advancing the die cut blank horizontally to a stripping position in which the scrap portion or portions overlie a stripping die with openings corresponding to the shape of the scrap (but slightly larger) and the remainder of the stripping die supporting the finished blank. A stripper is positioned above the scrap and die to make a linear downward stroke against the scrap and push it through the die and out of the blank. In one known flatbed stripper construction, the stripper plate includes a gridwork pattern on its underside in which downwardly extending stripper pins can be positioned by hand to define generally the outline of the scrap portion to be removed. When the stripper is stroked downwardly against the scrap, the pins engage the peripheral edge of the scrap portion and push it through the stripper die.
In a rotary die cutting process, the stripping process is also typically a rotary process. Thus, the die cut blank with the scrap portions intact is advanced past a rotary stripper roll which has a series of stripper pins attached to its cylindrical exterior, which pins are positioned to correspond to the outline of the scrap portion or portions and rotation of the stripper role is synchronized with the die cutting roll such that the stripper pins accurately engage and punch out the scrap from the blank as the blank is advanced from the die cutting station to the stripping station.
In the case of a flatbed die cutter, the stripper pins are typically positioned by hand to correspond to the shape of the scrap portion and the process is tedious and time consuming. These problems are aggravated where successive runs of blanks of different sizes and shapes are made, requiring frequent repositioning of the stripper pins.
In rotary strippers, a cylindrical metal sleeve is mounted to the outside of the stripper roll and a pattern or patterns of pins corresponding to the outlines of the scrap portion or portions are fixed to the surface of the metal sleeve. Each time a run of different blanks is made, the stripper pin sleeve must be removed from the roll and replaced with one accommodating the different scrap patterns of the new run. In a large volume operation the large number of stripper pin sleeves results in the need for a huge storage area and concomitant storage problems.
U.S. Pat. No. 3,524,364 discloses a rotary stripper apparatus in which the stripper pins force the scrap material portions into the surface of a soft covered counterrotating roll disposed on the opposite side of the blank. This apparatus provides positive stripping of the scrap, but requires an array of stripper pins corresponding to the outside shape of each scrap portion. Also, the pins are mounted on the cylindrical metal sleeve typical of prior art constructions.
U.S. Pat. No. 4,367,069 discloses a rotary stripping apparatus in which one of a pair of counter-rotating rolls has a series of extensible and retractable spikes having barbed ends which impale the scrap portion in cooperation with extensible and retractable abutments located on the other roll. Extension and retraction is provided by a suitable camming apparatus, all of which results in a mechanical apparatus which is rather complex and far too costly for use in small or one-time runs of die cut blanks.
U.S. Pat. No. 4,295,842 also utilizes a rotary stripper with pins having pointed outer ends to pierce and carry the scrap portions from the die cut blank. The scrap carried on the pins is subsequently stripped by carrying it past a stripper plate which causes the scrap to be pulled from the pins as the stripper roll rotates past it. Neither positive stripping of the scrap from the blank nor of the scrap from the pins is assured. Similarly, U.S. Pat. No. 2,647,446 utilizes stripper pins on a rotary drum which impale and carry the scrap portion from the blank to a rotationally displaced region where the scrap is stripped from the pins.
U.S. Pat. Nos. 4,474,565 and 4,561,334 disclose rotary die cutting apparatus in which the stripper mechanism is integral with the cutting die. Both utilize radially extensible stripper pins inside the cutting die which move outwardly and engage the scrap portions to eject them from the die cut blank. In the former patent, the ejector pins push the scrap from the blank and, in the latter, the pins penetrate the scrap portions which are then rotated out of the plane of the blank for mechanical stripping from the pins by a stripper blade adjacent the surface of the pin-carrying roll.
U.S. Pat. No. 3,956,974 similarly discloses a rotary stripping mechanism utilizing stripper pins which are axially extensible and retractable. The stripper pins, which are spring biased outwardly, are adapted to engage the scrap material, hold it against the surface of an opposing counterrotating roll, and force the scrap out of the plane of the blank as the pin and the adjacent surface of the roll rotate away from one another. The stripper pins are adjustable circumferentially to selectively variable positions and the mounting ring holding the pins is adjustable axially along the roll-supporting shaft to provide adjustable lateral positioning of the pins. This apparatus relies entirely on the stripper pins to completely strip the scrap portions from the blank.
U.S. Pat. No. 3,459,080 shows a rotary stripping apparatus in which the stripper pins are selectively embedded in a rigid semi cylindrical stripping die demountably attached to the surface of a stripper roll. The stripper pin pattern corresponds to the outline of the scrap portions to be stripped. The pins engage and push the scrap portions downwardly out of the advancing blank and the downwardly displaced scrap portions are caught under the edge of a stripper blade to positively ensure stripping of the scrap from the blank.